Sound systems are becoming increasingly advanced, complex and varied. For example, multi-channel spatial audio systems, such as five or seven channel home cinema systems, are becoming prevalent. However, the sound quality, and in particular the spatial user experience, in such systems is dependent on the relationship between the listening position and the loudspeaker positions. In many systems, the sound reproduction is based on an assumed relative speaker location and the systems are typically designed to provide a high quality spatial experience in a relatively small area known as the sweet spot. Thus, the systems typically assume that the speakers are located such that they provide a sweet spot at a specific nominal listening position.
However, the ideal speaker position setup is often not replicated in practice due to the constraints of practical application environments. Indeed, as loudspeakers are often considered to be a necessary rather than a desired design feature, users (such as private consumers) typically prefer a high flexibility in choosing the number and positions of loudspeakers. For example, in a typical living room, it is often not possible or desired (e.g. for aesthetic reasons) to position a high number of loudspeakers at the positions which result in optimal performance.
Some audio systems have been developed to include functionality for manual calibration and compensation for varying speaker positions. For example, many home cinema systems include means for manually setting a delay and relative signal level for each channel (e.g. by manually indicating the distance to the loudspeakers). However, such manual setting of individual parameters tends to be quite cumbersome and impractical for the typical user. Furthermore, it tends to not provide optimal performance as the parameters that can be set are relatively limited (while still being confusing to many non-experts).
It has also been proposed to perform a semi-automated automation process based on a microphone being placed at the listening position during a calibration process. The audio system may then optimize various characteristics of the signal path for each channel to provide optimized sound at the microphone position. However, although such a process may improve the audio quality it provides relatively limited flexibility as the optimization is only based on the information provided by the microphone, and as such is limited to one listening position and to adaptation of parameters that affect the sound captured by the microphone. For example, it does not provide any direct spatial information that can be used to optimize the system.
Some audio systems comprise functionality for optimizing the audio signal processing based on the actual speaker positions relative to a listening position or area. For example, systems have been proposed that automatically optimize the signal processing to provide the consumer with an optimized spatial sound reproduction for any loudspeaker configuration.
However, in order to optimize the sound reproduction in such a flexible system, it is necessary that the loudspeaker positions and preferably also the listening position and the orientation of the user are determined.
It has been proposed that the speaker positions can be automatically determined based on an acoustical measurement of the loudspeaker outputs. Specifically, it has been proposed that the relative positions of the loudspeakers may be determined by co-locating a microphone with each loudspeaker and with each loudspeaker then in turn playing a calibration signal that is picked up by the microphones of the other loudspeakers. By determining the different propagation delays from each individual loudspeaker to all the other loudspeakers from the captured signals, it is possible to make an estimation of the geometrical lay-out of the speaker setup.
However, such an approach has some associated disadvantages. For example, it requires additional hardware (a microphone) for each loudspeaker thereby increasing cost and limiting the use to systems wherein such microphones are provided with the speakers. Furthermore, it requires communication between the central unit and each of the loudspeakers thereby further increasing complexity and cost. In addition, the sensitivity to acoustical disturbances in the room is relatively high. For example, sound sources other than the loudspeakers or objects blocking the direct path from loudspeaker to microphones may degrade the approach significantly. Furthermore, the method requires a calibration signal to be played, which means the calibration process is noticeable and possibly annoying to the user. Also, in order to determine the listening position it is necessary to position an additional microphone at the listening position.
Another approach that has been proposed is RF (Radio Frequency) based localizing methods, such as RFID (Radio Frequency IDentification) and Ultra-wideband (UWB). These methods use tags that are attached to the objects to be localized. The tags emit a low-power RF signal which is detected by multiple (>=3) RF sensors, after which the relative location is determined by triangularization. However such an approach also has some associated disadvantages. In particular, each object to be localized needs to be tagged, multiple sensors are required and these need to be spatially distributed across the room, and the indoor-accuracy is often relatively low and insufficient for adapting audio systems to speaker configurations. Furthermore, the approach is relatively expensive as the cost of the associated technology is relatively high.
Furthermore, a common problem for most currently proposed approaches is that they are not easily extended from determining a speaker position to determining a position of a listener. For example, it is inconvenient to have to place and RFID sensor at a listening location.
Hence, an improved system for estimating speaker positions would be advantageous and in particular a system allowing increased flexibility, improved audio quality, reduced cost, facilitated operation, facilitated implementation, an improved user experience, an improved spatial perception and/or improved performance would be advantageous.